PROJECT SUMMARY/ABSTRACT Despite improvements in efficacy and coverage of antiretroviral therapy, the incidence of HIV in the United States (US) has failed to decline substantially in the last decade, while earlier declines in the incidence of other sexually transmitted infections (STIs) have recently reversed. As prevention dollars run short, it is important to identify strategies for efficiently investing resources to lower the burden of these interconnected epidemics. This mentored research scientist career development (K01) proposal would enable an accomplished junior candidate with expertise in agent-based simulation modeling to expand her skillset while describing network factors underpinning HIV transmission among men who have sex with men (MSM), modeling the epidemiological impact of combined prevention interventions for HIV and other STIs, and quantifying the cost- effectiveness of those interventions ? thus filling critical knowledge gaps in our current understanding of HIV/STI transmission and prevention in the US. The candidate's proposed research involves a rigorous, model-based investigation into the HIV/STI co- epidemic among MSM in Baltimore City ? a representative setting for which strong epidemiological and surveillance data exists. To understand the co-transmission dynamics of HIV and other STIs, the candidate will develop a series of contact networks using ten years of surveillance and contact investigation data available through Baltimore City Health Department (BCHD) and will quantify changes in the structure of this network over the last decade (Aim 1). To study and compare the impact of different prevention interventions on HIV/STI spread, the candidate will develop detailed models of STI co-transmission, including HIV, syphilis, gonorrhea and chlamydia. These models will be used to project the epidemiologic impact of targeting Pre-Exposure Prophylaxis (PrEP) to MSM diagnosed with other STIs and/or their sexual partners (Aim 2), and to assess the cost-effectiveness of strategies for PrEP implementation (Aim 3) at different levels of program coverage and individual uptake and adherence. The candidate for this award is a junior faculty member with a background in computational sciences who has more recently developed experience in HIV/AIDS research. During this award period, the candidate will be mentored by a multidisciplinary team of experts with complimentary skills in areas related to her research aims and training goals. Her K01 training goals are (1) to acquire expertise in analysis of social and sexual networks, (2) to develop a solid understanding of HIV/STI epidemiology and coinfection, (3) to gain experience in methods for economic evaluation, and (4) to improve her skills in mentorship, management, and collaboration with diverse stakeholders in order to achieve a successful transition to independence. Her long- term goal is to become an independent scientist developing and applying innovative analytical techniques to improve policies to help end the co-epidemics of HIV and other STIs among MSM in the US, and more broadly.